Solar cells provide a means to produce electric power with minimal environmental impact. In order to become a commercial success solar cells need to be efficient, to have low cost, to be durable, and to avoid causing other environmental problems.
Today's dominant solar cell technology is based on crystalline silicon. It fulfils many of the requirements mentioned above but crystalline silicon solar cells can not readily be produced at such a low cost that large scale power generation is cost effective. They also require relatively large amounts of energy to manufacture them, which is an environmental disadvantage.
Solar cells based on thin film technologies have been developed. They offer the potential for substantial cost reductions but have, in general, lower conversion efficiencies and less durability than crystalline silicon solar cells. A very promising thin film solar cell technology is based on a semiconductor CIGS layer, which has demonstrated high efficiency (16.6% in small prototype modules) and durability in operation. However, this technology has yet to demonstrate that it can produce cells commercially at a low cost. CIGS is an abbreviation for the typical alloying elements in the semiconductor material, i.e. Cu, In, Ga, Se and S, forming a Cu(In1-xGax)Se2 compound. Commonly a CIGS layer also comprises sulphur, i.e. Cu(In1-xGax)(Se1-ySy)2.
A typical CIGS solar cell comprises a CIGS layer on a substrate material such as sheet glass or metal foil, which has been coated with a layer of molybdenum. This layer serves as the back contact of the solar cell. The CIGS growth is followed by the formation of a pn-junction by deposition of a buffer layer, typically 50 nm of CdS, optionally a high resistivity thin layer of ZnO and a front contact made of a transparent conductive oxide, e.g. of Al-doped ZnO (ZAO). The buffer layer of CdS may be exchanged for e.g. a ZnOzY1-z layer.
CIGS-based thin film solar cells are commonly fabricated by high vacuum co-evaporation of the elements Cu, In, Ga and Se. By way of example, a prior art method for manufacturing a thin film solar cell module that comprises a plurality of serially-connected longitudinal solar cells comprises the steps of:                providing a substrate with a Mo-coating that is divided into longitudinal segments;        depositing the CIGS layer on the Mo-coated substrate using an in-line production apparatus and subsequently depositing the buffer layer and the high resistivity layer onto the CIGS layer;        forming grooves in the semiconductor layers, commonly by using a mechanical stylus, to form longitudinal segments parallel with, and overlapping, the longitudinal segments in the Mo-coating;        depositing a front contact on the top surface of the segmented semiconductor layers; and        providing an array of serially-connected longitudinal segments by patterning, i.e. forming grooves in, the front contact and the underlying semiconductor layers using a mechanical stylus.        
The next step is to make a useful thin film solar cell device out of this thin film solar cell module. To be able to reliably perform electrical insulation and hermetic sealing of the solar cell module, all thin film layers on top of the glass substrate of the thin film solar cell module in a circumferential region are usually completely removed in a so-called “edge deletion” operation. Laser ablation, sand blasting and grinding are currently used edge deletion methods. The edge deletion makes it possible to obtain a hermetic seal against the glass in the peripheral region which prevents corrosion of the thin film layers of the solar cell module. Electrical insulation is also necessary to prevent current leakage and short circuit.
Furthermore the edge deletion operation is usually followed by contacting, so-called “edge tabbing”, of the conducting uppermost layer (front contact) of the solar cells using e.g. conductive glue and copper strips, lamination, framing and mounting of a junction box to which cables can be connected. The so-called “tab wires” can be lead to the junction box e.g. through holes drilled in the substrate or via the edges of the substrate.
The challenging edge deletion and edge tabbing operations are important issues for making reliable thin film solar cell devices. The current development of thin film solar cell devices requires efficient processes with high throughput to obtain low cost, high performance solar cell devices. Mean for lowering the cost includes an increase of the surface area of the solar cell modules. Accordingly, high removal rates in the edge deletion operation are required, with maintained, or preferably improved, accuracy and cleanliness. The durability and the performance of the final solar cell devices may be seriously reduced if residuals from the edge deletion step are left on the solar cell modules until contacting and lamination. Consequently cleaning operations, increasing the processing time and limiting the throughput, are usually required. In addition the dust from the machining operation may be hazardous and needs to be collected and disposed of safely.